Active current monitor

ABSTRACT

A current monitor for a transmission line having powered active components is provided. A current monitor includes: a housing configured to be coupled to a transmission line, an inductive current sensor in the housing configured to measure a value of the current on the transmission line to generate a sensor signal, a power source, and a sensor signal conversion circuit in the housing configured to receive power from the power source and to generate a current output signal based on the sensor signal, the current output signal having a natively useful form.

FIELD

Aspects of embodiments of the present invention relate to a wirelesscurrent and voltage monitoring insulator, and a high-accuracy voltagemeasuring resistor assembly.

BACKGROUND

A post insulator functions as a mechanical support between atransmission line and an electrical pole or tower while electricallyinsulating the transmission line from the pole or tower. For example,the post insulator may be mountable on a crossarm of an electrical poleand may be made of a ceramic or other suitable electrically insulativematerial. The transmission line, or conductor, may be supported on thepost insulator by any of various devices, such as via bus bars, clamps,a tube-type support (e.g., the conductor may run through a tube in thepost insulator), or a channel in the post insulator.

For various reasons, it may be desirable to obtain measurements ofvoltage and/or current of a conductor supported by a post insulator. Insuch instances, it may also be desirable that the voltage and/or currentmeasurements have high accuracy and that the information may be easilytransmitted. It is also desirable that voltage and/or current sensorsfor providing such measurements be reliable.

SUMMARY

According to an aspect of embodiments of the present disclosure, acurrent sensor having high accuracy and reliability is provided in apost insulator.

According to an aspect of the present disclosure, a current monitor isdisclosed. The current monitor includes a housing configured to becoupled to an electric power line; an inductive current sensor in thehousing configured to measure a value of a current on the electric powerline to generate a sensor signal; a power source; and a sensor signalconversion circuit in the housing configured to receive power from thepower source and to generate a current output signal based on the sensorsignal.

In some embodiments, the sensor signal conversion circuit utilizes thereceived power to generate the current output signal such that thecurrent output signal has a natively useful form.

In some embodiments, the sensor signal includes a gain change and aphase shift, and the sensor signal conversion circuit compensates thegain change and the phase shift to generate the current output signalsuch that the current output signal represents the value of the currenton the electric power line with a constant gain and zero phase shift.

In some embodiments, the inductive current sensor does not fullysurround the electric power line.

In some embodiments, the sensor signal conversion circuit comprises atleast one active circuit element powered by the power from the powersource, and the sensor signal conversion circuit utilizes the activecircuit element for generating the current output signal.

In some embodiments, the current monitor includes a voltage sensor inthe housing configured to measure a value of a voltage on the electricpower line to generate a voltage sensor signal, the sensor signalconversion circuit being further configured to generate a voltage outputsignal based on the voltage sensor signal.

In some embodiments, the sensor signal conversion circuit comprises atleast one active circuit element powered by the power from the powersource, and the sensor signal conversion circuit utilizes the activecircuit element for generating the voltage output signal.

In some embodiments, the sensor signal conversion circuit comprises atemperature conversion circuit powered by the power from the powersource, and the sensor signal conversion circuit utilizes thetemperature conversion circuit to generate the current output signal.

In some embodiments, the power source is the electric power line, thecurrent monitor comprises a power resistor in the housing coupled to theelectric power line configured to generate a power voltage from anelectric power line voltage, and the sensor signal conversion circuit isconfigured to receive the power voltage.

In some embodiments, the sensor signal conversion circuit is configuredto utilize the power voltage to generate the current output signal whenlittle or no current is present on the electric power line.

In some embodiments, the current monitor includes a sensing resistor inthe housing coupled to the electric power line configured to generate avoltage sensor signal, wherein the sensor signal conversion circuit isconfigured to generate a voltage output signal based on the voltagesensor signal.

In some embodiments, the power resistor shields the sensing resistorfrom noise or environmental temperature variation.

In some embodiments, the current monitor includes a second sensingresistor in the housing, wherein the power resistor shields the secondsensing resistor from noise or environmental temperature variation, thesensing resistor is connected between the electric power line and thesecond sensing resistor, the second sensing resistor is connectedbetween the sensing resistor and a common voltage, and a voltage acrossthe second sensing resistor is utilized to generate the voltage sensorsignal.

In some embodiments, the sensor signal conversion circuit is configuredto utilize the power voltage to generate the voltage output signal whenlittle or no current is present on the electric power line.

In some embodiments, the current on the electric power line has a powertransmission frequency, and the current output signal comprises thevalue of the current on the electric power line at frequencies otherthan the power transmission frequency.

In some embodiments, the current output signal comprises a harmoniccomponent of the current on the electric power line.

In some embodiments, the current output signal represents the current onthe electric power line with an error of less than 0.2%.

In some embodiments, the housing is an insulator body configured toelectrically isolate the electric power line from an electric power linesupport.

In some embodiments, the current monitor includes an output circuitconfigured to communicate the current output signal to an externaltransceiver.

In some embodiments, the output circuit comprises a surface acousticwave device.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription and accompanying drawings where:

FIG. 1 is a schematic view of a current and voltage monitoring insulatoraccording to an embodiment of the present invention;

FIG. 2A is a cross section of a current monitor illustrating a dual-coreinductive current sensor according to embodiments of the presentdisclosure.

FIG. 2B is a cross section of a current monitor illustrating asingle-core inductive current sensor according to embodiments of thepresent disclosure.

FIG. 2C is a cross section of a current monitor illustrating a Rogowskicoil current sensor according to embodiments of the present disclosure.

FIG. 3 is a block diagram of a current and voltage monitor according toembodiments of the present disclosure.

FIG. 4A is a graph showing the gain at different frequencies of arelated art sensor device.

FIG. 4B is a graph showing the gain at different frequencies of a sensorsignal conversion circuit according to embodiments of the presentdisclosure.

FIG. 4C is a graph showing the phase shift at different frequencies of arelated art sensor device.

FIG. 4D is a graph showing the phase shift at different frequencies of asensor signal conversion circuit according to embodiments of the presentdisclosure.

FIG. 5 is a block diagram of a current and voltage monitor according toembodiments of the present disclosure.

FIG. 6A is an isometric cross section view of a current and voltagemonitor according to embodiments of the present disclosure.

FIG. 6B is a side cross section view of a current and voltage monitoraccording to embodiments of the present disclosure.

FIG. 7 is an isometric cross section view of a current and voltagemonitor according to embodiments of the present disclosure.

FIG. 8 is a cross section view of a transmission line interfaceaccording to embodiments of the present disclosure.

DETAILED DESCRIPTION

In the following detailed description, certain exemplary embodiments ofthe present invention are shown and described, by way of illustration.As those skilled in the art would recognize, the described exemplaryembodiments may be modified in various ways without departing from thespirit and scope of the present invention. Accordingly, the drawings anddescription are to be regarded as illustrative in nature, rather thanrestrictive.

FIG. 1 is a current and voltage monitor 100 according to embodiments ofthe present disclosure. While the term “current and voltage monitor”will be used throughout the specification, it is noted that in someembodiments, the current and voltage monitor may include currentmonitoring capabilities without voltage monitoring capabilities, or mayinclude both current and voltage monitoring capabilities. The currentand voltage monitor 100 includes a housing 110 which encloses a currentsensor. The current and voltage monitor 100 may be installed on or nearan electric power line used for distribution or transmission(hereinafter “a transmission line”) 140 in order to measure the currentpresent on the transmission line 140. In some embodiments, the currentand voltage monitor 100 is mounted on the transmission line andsupported by the transmission line (i.e., hanging from or wrapped aroundthe transmission line). In some embodiments, the current and voltagemonitor 100 is mounted on a transmission line support such as atransmission line pole or a crossarm in proximity to the transmissionline 140, and the housing 110 may contact the transmission line or mayhave one or more lead extending from the housing 110 to the transmissionline 140. In some embodiments, the housing of the current and voltagemonitor 100 supports the transmission line 140.

In the embodiment shown in FIG. 1, the current and voltage monitor 100includes a housing 110, a recess 120, and a keeper 130. The housing 110is an insulator body made of an insulating material. The insulator bodymay be utilized as a post insulator to be mounted on a crossarm of atransmission line pole or tower. The housing 110, according to anembodiment, may have a recess 120 into which the conductor 140 may bereceived. That is, an upper region of the housing 110 may be U-shapedwhen viewed from a first side to define the recess 120 that extends fromthe first side to an opposite side. As such, the conductor 140 may belifted into the recess 120 and supported by the current and voltagemonitor 100 without being cut or requiring a jumper. However, thepresent invention is not limited thereto, and aspects of the presentinvention may also be applied to another type of post insulator, such asone having bus bars or clamps, for example.

The housing 110, in an exemplary embodiment, may be made of Polysil, ahigh dielectric strength polymer known and available to those skilled inthe art. However, the present invention is not limited thereto, and, inother embodiments, the insulator 130 may be made of a hydrophobiccycloaliphatic epoxy (HCEP) or other suitable epoxy, for example.

The current and voltage monitor 100 may include a keeper 130 and, in anembodiment, may include a pair of keepers 130 at opposite sides of therecess 120. The keeper or keepers 130 may be configured to be removablycoupled to housing 110 to retain the transmission line 140 in the recess120.

In some embodiments, the keeper 130 is configured to provide a contactfor electrically connecting to the transmission line from inside thehousing 110. For example, the keeper 130 may be made of or may include aconductive material, and may attach to the housing 110 by boltsconfigured to be threadedly engaged in a respective pair of the threadedinserts. The keeper 130, the bolts, and the threaded inserts may allinclude conductive materials providing an electrical path between thetransmission line in contact with the keeper and the inside of thehousing 110.

The current sensor contained in the housing 110 may be an inductivecurrent sensor. In particular, the current sensor may be an inductivesensor that does not fully encircle the transmission line 140 in orderto facilitate depositing the transmission line 140 in the recess 120without cutting the transmission line 140 or requiring a jumper.

FIGS. 2A-2C show different embodiments of a current sensor according toembodiments of the present disclosure. FIG. 2A is a cross section of acurrent monitor illustrating a dual-core inductive current sensor 210 aaccording to embodiments of the present disclosure. The dual-coreinductive current sensor 210 a includes first and second inductive coilsplaced on opposite sides of the recess 120. Because the transmissionline 140 is seated in the recess 120, the first and second inductivecoils can be placed directly on either side of the transmission line140. The current flowing in the transmission line 140 generates amagnetic field which in turn induces current in the dual-core inductivecurrent sensor 210 a, and the induced current is used as a currentsensor signal or utilized to generate the current sensor signal.

FIG. 2B is a cross section of a current monitor illustrating asingle-core inductive current sensor 210 b according to embodiments ofthe present disclosure. The single-core inductive current sensor 210 bincludes a single inductive coil. The inductive coil may be placed atany point adjacent to the conductor 140. In some embodiments, the recess120 is shallow, such that the sides of the recess are shorter than thecircumference of the transmission line 140, and the single-coreinductive current sensor 210 b is placed directly beneath the recess120. The current flowing in the transmission line 140 generates amagnetic field which in turn induces current in the single-coreinductive current sensor 210 a, and the induced current is used as acurrent sensor signal or utilized to generate the current sensor signal.

FIG. 2C is a cross section of a current monitor illustrating a Rogowskicoil current sensor 210 c according to embodiments of the presentdisclosure. The Rogowski coil 210 c may be a single-turn, open-loop leadand a wire connected to one end of the open-loop lead and coiled aroundthe lead along the length of the lead toward the other end. Thesingle-turn, open-loop lead of the Rogowski coil 210 c may have aU-shape and be oriented along the U-shape of the recess 120. The currentflowing in a transmission line 140 in the recess 120 may induce acurrent in the Rogowski coil 210 c which may be used as the currentsensor signal or may be utilized to generate the current sensor signal.The current sensor signal generated by the Rogowski coil 210 c may be aderivative of the current on the transmission line 140, and maytherefore not be natively useful to other components of the current andvoltage monitor 100.

Some portion of the current sensor signal, or the entire current sensorsignal, generated by the current sensor may not be natively useful toother components of the current and voltage monitor 100 (e.g., fordetermining the current on the transmission line, communicating thedetermined current, or performing an action based on the determinedcurrent) without further processing. For example, the current sensorsignal from the dual-core inductive current sensor 210 a may have alinear gain, but may exhibit non-linear phase shift at differentfrequencies. The characteristics of the current sensor signal from thesingle-core inductive current sensor 210 b may vary based on thediameter of the conductor (i.e., the larger the conductor, the furtherthe center of the conductor from the current sensor). The current sensorsignal from the Rogowski coil 210 c may be a derivative of the currenton the transmission line 140.

FIG. 3 is a block diagram of a current monitor according to embodimentsof the present disclosure. The current monitor includes a current sensor210, a power source 310, a power supply 320, a sensor signal conversioncircuit 390, and an output circuit 350.

The sensor signal conversion circuit 390 and/or the output circuit mayinclude active components. The power supply 320 utilizes power from thepower source 310 to generate one or more supply voltage for the activecomponents of sensor signal conversion circuit and/or output circuit. Insome embodiments, the power source 310 may be a power resistoroutputting a power voltage from the transmission line voltage, asdiscussed below in more detail. In other embodiments, the power source310 may additionally or alternatively be a battery, a solar panel, aninductive energy harvesting circuit, or a combination thereof.

The current sensor 210 is an inductive current sensor which generates acurrent sensor signal based on the magnetic field generated by thecurrent on the transmission line 140, such as the dual-core inductivecurrent sensor 210 a, the single-core inductive current sensor 210 b, orthe Rogowski coil 210 c discussed above. The current sensor 210 does notcompletely enclose the transmission line 140. Accordingly, the currentsensor signal generated by the current sensor 210 may not be nativelyuseful (e.g., useful to the output circuit 350) without furtherprocessing.

The sensor signal conversion circuit 390, utilizing active componentspowered by the supply voltage from the power supply 320, receives thecurrent sensor signal from the current sensor 210 and processes thecurrent sensor signal into a current output signal which can be utilizedby the output circuit 350, and passes the current output signal to theoutput circuit 350.

In one embodiment, the sensor signal conversion circuit 390 includes again circuit 330 and a phase adjust circuit 340. The gain circuit 330receives the current sensor signal from the current sensor 210. FIG. 4Ashows the gain at different frequencies of a related art sensor devicewhich does not include a gain circuit 330. As can be seen, the gain maybe different at different frequencies, and the device may be configuredto have peak gain at the power transmission frequency (e.g., 60 Hz). Acurrent sensor signal generated from such a configuration may includeinformation about the power at the power transmission frequency, but maylose information related to the harmonic components located at higherand lower frequencies which may reduce the accuracy of the reading ormay lose specific information provided by the harmonic components. Inembodiments of the present disclosure where the gain circuit 330utilizes active components, powered with the supply voltages generatedby the power supply 320, the gain circuit 330 can provide unity gainacross the relevant frequency spectrum as shown in FIG. 4B. As a result,harmonic components of the current on the transmission line containinginformation which may be desirable to monitor may be preserved andincluded in the current output signal. Passive gain components mayprovide gain at the frequency of the transmission line current, but maynot provide the same gain to the harmonics, and this information may belost.

The phase adjust circuit 340 may receive the output of the gain circuit330. FIG. 4C shows the phase shift at different frequencies of a relatedart sensor device which does not include a phase adjust circuit 340. Ascan be seen, the phase shift may be different at different frequencies,and the device may be configured to have zero phase shift at the powertransmission frequency (e.g., 60 Hz). Components of the current on thetransmission line at frequencies other than the power transmissionfrequency such as the harmonic components may be subject to phase shift,and therefore may not be captured or may not be actionable or otherwiseuseful without further processing. In embodiments of the presentdisclosure where the phase adjust circuit 340 utilizes activecomponents, powered with the supply voltages generated by the powersupply 320, the phase adjust circuit 340 may process the current sensorsignal to provide zero phase shift across the entire frequency spectrumof interest as shown in FIG. 4D. As a result, harmonic components of thecurrent on the transmission line may be recovered and/or actionable oruseful.

The sensor signal conversion circuit 390 may additionally oralternatively include other active components for converting the currentsensor signal into a natively useful current output signal, includingbut not limited to an integrator, a differentiator, a temperaturecompensation circuit, and/or an equation-based non-linear transformcircuit. In one embodiment, the current sensor 210 is a Rogowski coiland the sensor signal conversion circuit 390 includes an activeintegration circuit to compensate for the transfer function of theRogowski coil. In some embodiments, such as embodiments utilizing thesingle-core inductive current sensor 210 b, the sensor signal conversioncircuit 390 generates the current output signal by compensating thecurrent sensor signal based on the distance from the center of thetransmission line (e.g., based on the diameter of the conductor).

In some embodiments, the sensor signal conversion circuit 390 generatesthe current output signal such that it represents the current on thetransmission line with an error of less than 1%. In some embodiments,the sensor signal conversion circuit 390 generates the current outputsignal such that it represents the current on the transmission line withan error of less than 0.2% and the voltage and current monitor is usedfor revenue metering applications. In some embodiments, the sensorsignal conversion circuit 390 is able to generate the current outputsignal such that it represents the current on the transmission line withan error of less than 0.2%, e.g., by accounting for the harmoniccomponents of the current on the transmission line in the current outputsignal utilizing an active gain circuit and/or an active phase shiftcircuit. In some embodiments, the sensor signal conversion circuit 390generates the current output signal such that it represents the currenton the transmission line with an error of less than 0.2% by utilizing anactive gain circuit and/or an active phase shift circuit to recover theharmonic components of the line current and by utilizing a temperaturecompensation circuit to correct for temperature variations.

The output circuit 350 performs an output action based on the currentoutput signal. In some embodiments, the output circuit 350 stores thevalue of the current on the transmission line in a database, where thevalue of the current on the transmission line is determined based on thevalue of the current output signal. In some embodiments, the outputcircuit 350 includes a radio and the radio transmits the current outputsignal or the value of the current on the transmission line (derivedfrom the current output signal) to an external receiver. In someembodiments, the output circuit 350 includes a line driver powered bythe supply voltage from the power supply 320, and the line driver isused to transmit the current output signal or the value of the currenton the transmission line. In some embodiments, the output circuit 350includes a fiber optic communication circuit powered by the supplyvoltage from the power supply 320, and the fiber optic communicationcircuit is used to transmit the current output signal or the value ofthe current on the transmission line.

In some embodiments, the output circuit 350 includes an RFID circuitconfigured to communicate the value of the current on the transmissionline, the value of the current output signal, or another measurement toan external transceiver. In some embodiments, the RFID circuitcommunicates an identifier (e.g., a unique identifier) for the currentand voltage monitor 100 with the value or measurement. In someembodiments, the RFID circuit utilizes a surface acoustic wave (“SAW”)device to perform signal processing and/or to take measurements to becommunicated to the external transceiver. For example, this can beaccomplished using SAW devices available from SenSanna.

FIG. 5 is a block diagram of a current and voltage monitor according toembodiments of the present disclosure.

The current and voltage monitor of FIG. 5 includes a current sensor 210sensing the current on a transmission line 140, a transmission linevoltage interface 410, a power supply 420, a voltage sensor signalconversion circuit 430, a current sensor signal conversion circuit 440,and an output circuit 450.

The transmission line 140 and the transmission line voltage interface410 may act as a power source. The transmission line voltage interface410 generates a power voltage and a scaled voltage from the transmissionline voltage. The power supply 420 utilizes the power voltage togenerate one or more supply voltages which it provides to the voltagesensor signal conversion circuit 430 and the current sensor signalconversion circuit 440. When no power is delivered through atransmission line, the transmission line may still have its normaloperating voltage level, but may have no current or a low level ofcurrent passing through the transmission line. In such circumstances,systems which generate power from the current on a transmission line(e.g., by inductively harvesting power) may not be able to generatepower and may therefore be inoperative. Generating the power voltagefrom the transmission line voltage may allow the current and voltagemonitor to generate the power voltage, and thereby remain operative,even when no power is being delivered through the transmission line.

The voltage sensor signal conversion circuit 430 utilizes the scaledvoltage as a voltage sensor signal and generates a voltage outputsignal. In some embodiments, the voltage sensor signal conversioncircuit 430 utilizes active components powered with a supply voltagefrom the power supply 420 to generate the voltage output signal. Thecurrent sensor signal conversion circuit 440 receives a current sensorsignal from the current sensor 210, and utilizes active componentspowered with a supply voltage from the power supply 420 to generate acurrent sensor output signal. The sensor signal conversion circuits 430and 440 pass the voltage output signal and the current output signal tothe output circuit 450.

FIG. 6A is an isometric cross section view of a current and voltagemonitor 100 according to embodiments of the present disclosure, and FIG.6B is a side cross section view of the current and voltage monitor 100.With reference to FIGS. 6A and 6B, the current and voltage monitor mayinclude one or more contacts 136, a current sensor 210, a transmissionline voltage interface 220, an electronics package 230, and the housing110. Shielded wires may be used to electrically connect elements insidethe housing 110 in order to prevent or reduce noise (e.g., from thetransmission line 140 or neighboring transmission lines). The housing110 houses (e.g., encapsulates) the transmission line voltage interface220, the electronics package 230, and/or the current sensor 210.

One or more contacts 136 may provide a conductive pathway forelectrically connecting objects inside the housing 110 with thetransmission line 140. In some embodiments, the contact 136 is athreaded insert which threadedly engages a conductive bolt. Theconductive bolt may be used to couple the current and voltage monitor100 to the transmission line 140, such as described above with respectto the keeper, bolt, and threaded inserts of FIG. 1. In someembodiments, all of the contacts 136 may be tied together at a commonpotential.

The power source of FIGS. 6A and 6B may be the transmission line 140and/or the transmission line voltage interface 220. The transmissionline voltage interface 220 may electrically connect components of thecurrent and voltage monitor 100 to the voltage on the transmission line140 without causing the components to be damaged by the potentially highpower present. In some embodiments, the transmission line voltageinterface 220 includes a power resistor 222. The power resistor may beelectrically coupled to the transmission line 140, for example by beingelectrically coupled to the contact 136, and configured to output apower voltage. The power voltage may be used to power components in thecurrent and voltage monitor 100, which will be described in more detailbelow. In some embodiments, the transmission line voltage interface 220includes a sensing resistor 224. The sensing resistor 224 may beelectrically coupled to the transmission line 140, for example by beingelectrically coupled to a contact 136 or by being connected to the powervoltage output from a power resistor 222. The sensing resistor 224 maybe configured to output a voltage sensor signal corresponding to thevoltage level on the transmission line 140.

The current sensor 210 c depicted in FIGS. 6A and 6B is a Rogowski coil(e.g., a coil with an open-loop lead and a wire connected to one end ofthe open-loop lead and coiled around the lead along the length of thelead toward the other end). The open-loop lead of the Rogowski coil maybe oriented along the U-shape of the recess 120. FIG. 7 shows anisometric cross section view of another embodiment of a current andvoltage monitor according to the present disclosure, where the currentsensor 210 a includes first and second inductor coils in a dual-corecurrent sensor arrangement. The first and second inductor coils 210 aare positioned on opposite sides of the recess 120.

Referring again to FIGS. 6A and 6B, the electronics package 230 may belocated at an end of the housing 110 opposite the end which is incontact with the transmission line 140. A ground port may be coupled toan external ground and may connect the electronics package 230 to theexternal ground. The electronics package 230 may receive a voltagesensor signal and/or a power voltage from the transmission line voltageinterface 220, and a current sensor signal from the current sensor 210.

The electronics package 230 may include the sensor signal conversioncircuit, including a current sensor signal conversion circuit and/or avoltage sensor signal conversion circuit. The electronics may alsoinclude an output circuit, e.g., a communication circuit. Any of thecircuits in the electronics package 230 may be powered by the powervoltage generated from the voltage on the transmission line by thetransmission line voltage interface 220. The sensor signal conversioncircuit may receive the current sensor signal from the current sensor210 and may generate a current output signal based on the current sensorsignal. Similarly, the sensor signal conversion circuit may receive thevoltage sensor signal from the sensing resistor 224 and may generate avoltage output signal based on the voltage sensor signal. In someembodiments, the voltage sensor signal from the sensing resistor 224 canbe used directly as the voltage output signal. In other embodiments, thevoltage sensing circuit only includes a gain step for converting thevoltage sensor signal to the voltage output signal. The communicationcircuit may be connected to an antenna, and may utilize the antenna totransmit the current output signal and/or the voltage output signal to areceiver. The antenna may be near to an outer surface of the housing 110such that a signal may be transmitted easily to the receiver.

FIG. 8 is a cross section view of a transmission line voltage interface220 according to embodiments of the present disclosure. The transmissionline voltage interface 220 comprises a power resistor 222, and a firstsensing resistor 224, and a second sensing resistor 226. The powerresistor 222 may have a cylindrical or substantially cylindrical shapewith an inner cavity defined through the middle of the power resistor222 and openings at both ends (e.g., a tube shape). The ends of thepower resistor 222 may be used as the terminals, and one terminal may beelectrically connected to the transmission line to receive atransmission line voltage V_(TRANSMISSION LINE) and the other may outputa power voltage V_(POWER), for example to the electronics package 230.The first sensing resistor 224 and the second sensing resistor 226 maybe positioned inside the inner cavity of the power resistor 222. Forexample, the first sensing resistor 224 and/or the second sensingresistor 226 may have a rod shape which runs coaxially or substantiallycoaxially with the length of the cavity and the ends of the rod shapemay be used as the terminals. One terminal of the first sensing resistor224 may be electrically connected to the transmission line to receive atransmission line voltage V_(TRANSMISSION LINE) and the other may beelectrically connected to a terminal of the second sensing resistor 226.The other terminal of the second sensing resistor 226 may beelectrically connected to ground. A scaled voltage V_(SCALED) can bemeasured across the second sensing resistor 226, for example by theelectronics package 230.

The voltage drop across a resistor such as the second sensing resistor226 may be influenced by noise (e.g., electrical fields) from outsidesources, capacitive coupling with external objects, and/or thetemperature of the surrounding environment. The transmission linevoltage interface 220 of FIG. 8 may utilize the first sensing resistor224 and the second sensing resistor 226 to generate a very accuratescaled voltage V_(SCALED) to determine the voltage on the transmissionline. As the power resistor 222 surrounds the first sensing resistor 224and the second sensing resistor 226, it may shield the first sensingresistor 224 and the second sensing resistor 226 from noise, such asnoise from the transmission line 140 or from neighboring transmissionlines, preventing that noise from impacting the scaled voltageV_(SCALED). Capacitive coupling may be present between the transmissionline voltage interface 220 and the housing 110, especially where thehousing 110 is wet, such as when it rains. Where there is capacitivecoupling between the transmission line voltage interface 220 and outsideelements such as the housing 110, the capacitive coupling is with thepower resistor 222, and thereby has a reduced or a nonexistent impact onthe scaled voltage V_(SCALED). The power resistor 222 may heat up duringoperation, and thereby heat its inner cavity. The heated inner cavitymay provide a temperature environment for the first sensing resistor 224and the second sensing resistor 226 which has a smaller range ofpossible temperatures than the environmental temperature where thecurrent and voltage monitor 100 is installed. Accordingly, thetransmission line voltage interface 220 may reduce or eliminatevariations in the scaled voltage V_(SCALED) caused by environmentaltemperature changes. As a result, the current and voltage monitor 100utilizing the transmission line voltage interface 220 may measure thevoltage on the transmission line with an error of less than 0.2%.

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondescribed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of thepresent invention.

Although the drawings and accompanying description illustrate certainexemplary embodiments of the present invention, it will be apparent thatthe novel aspects of the present invention may also be carried out byutilizing alternative structures, sizes, shapes, and/or materials inembodiments of the present invention. Also, in other embodiments,components described above with respect to one embodiment may beincluded together with or interchanged with those of other embodiments.Accordingly, persons skilled in the art and technology to which thisinvention pertains will appreciate that alterations and changes in thedescribed structures and methods of operation can be practiced withoutmeaningfully departing from the principles, spirit, and scope of thisinvention.

What is claimed is:
 1. A current monitor comprising: a housingconfigured to be coupled to an electric power line; an inductive currentsensor in the housing configured to measure a value of a current on theelectric power line to generate a sensor signal; a power source; and asensor signal conversion circuit in the housing configured to receivepower from the power source and to generate a current output signalbased on the sensor signal, wherein: the power source is the electricpower line, the current monitor comprises a power resistor in thehousing, coupled to the electric power line, and configured to generatea power voltage from an electric power line voltage, the sensor signalconversion circuit is configured to receive the power voltage, and thesensor signal conversion circuit is configured to utilize the powervoltage to generate the current output signal, even when no power isdelivered through the electric power line.
 2. The current monitor ofclaim 1, wherein the sensor signal conversion circuit comprises at leastone active circuit element powered by the power from the power source,and wherein the sensor signal conversion circuit utilizes the activecircuit element for generating the current output signal, and thecurrent output signal represents the current on the electric power linewith an error of less than 0.2%.
 3. The current monitor of claim 1,wherein the sensor signal conversion circuit utilizes the received powerto generate the current output signal such that the current outputsignal has a form useable by an output circuit of the current monitorwithout further processing.
 4. The current monitor of claim 1, whereinthe sensor signal includes a gain change and a phase shift, and whereinthe sensor signal conversion circuit compensates the gain change and thephase shift to generate the current output signal such that the currentoutput signal represents the value of the current on the electric powerline with a constant gain and zero phase shift.
 5. The current monitorof claim 1, wherein the inductive current sensor does not fully surroundthe electric power line.
 6. The current monitor of claim 1, furthercomprising a voltage sensor in the housing configured to measure a valueof a voltage on the electric power line to generate a voltage sensorsignal, the sensor signal conversion circuit being further configured togenerate a voltage output signal based on the voltage sensor signal. 7.The current monitor of claim 6, wherein the sensor signal conversioncircuit comprises at least one active circuit element powered by thepower from the power source, and wherein the sensor signal conversioncircuit utilizes the active circuit element for generating the voltageoutput signal.
 8. The current monitor of claim 1, wherein the sensorsignal conversion circuit comprises a temperature conversion circuitpowered by the power from the power source, and wherein the sensorsignal conversion circuit utilizes the temperature conversion circuit togenerate the current output signal.
 9. The current monitor of claim 1,further comprising a sensing resistor in the housing, coupled to theelectric power line, and configured to generate a voltage sensor signal,wherein the sensor signal conversion circuit is configured to generate avoltage output signal based on the voltage sensor signal.
 10. Thecurrent monitor of claim 1, wherein the current on the electric powerline has a power transmission frequency, and wherein the current outputsignal comprises the value of the current on the electric power line atfrequencies other than the power transmission frequency.
 11. The currentmonitor of claim 1, wherein the current output signal comprises aharmonic component of the current on the electric power line.
 12. Thecurrent monitor of claim 1, wherein the housing is an insulator bodyconfigured to electrically isolate the electric power line from anelectric power line support.
 13. The current monitor of claim 1, furthercomprising an output circuit configured to communicate the currentoutput signal to an external transceiver.
 14. The current monitor ofclaim 13, wherein the output circuit comprises a surface acoustic wavedevice.
 15. A current monitor comprising: a housing configured to becoupled to an electric power line; an inductive current sensor in thehousing configured to measure a value of a current on the electric powerline to generate a sensor signal; a power source; and a sensor signalconversion circuit in the housing configured to receive power from thepower source and to generate a current output signal based on the sensorsignal, wherein: the power source is the electric power line, thecurrent monitor comprises a power resistor in the housing, coupled tothe electric power line, and configured to generate a power voltage froman electric power line voltage, the sensor signal conversion circuit isconfigured to receive the power voltage, the current monitor furthercomprises a sensing resistor in the housing coupled to the electricpower line configured to generate a voltage sensor signal, wherein thesensor signal conversion circuit is configured to generate a voltageoutput signal based on the voltage sensor signal, and the power resistorshields the sensing resistor from noise or environmental temperaturevariation.
 16. The current monitor of claim 15, further comprising asecond sensing resistor in the housing, wherein: the power resistorshields the second sensing resistor from noise or environmentaltemperature variation, the sensing resistor is connected between theelectric power line and the second sensing resistor, the second sensingresistor is connected between the sensing resistor and a common voltage,and a voltage across the second sensing resistor is utilized to generatethe voltage sensor signal.
 17. A current monitor comprising: a housingconfigured to be coupled to an electric power line; an inductive currentsensor in the housing configured to measure a value of a current on theelectric power line to generate a sensor signal; a power source; and asensor signal conversion circuit in the housing configured to receivepower from the power source and to generate a current output signalbased on the sensor signal, wherein: the power source is the electricpower line, the current monitor comprises a power resistor in thehousing, coupled to the electric power line, and configured to generatea power voltage from an electric power line voltage, the sensor signalconversion circuit is configured to receive the power voltage, thecurrent monitor further comprises a sensing resistor in the housingcoupled to the electric power line configured to generate a voltagesensor signal, wherein the sensor signal conversion circuit isconfigured to generate a voltage output signal based on the voltagesensor signal, and the sensor signal conversion circuit is configured toutilize the power voltage to generate the voltage output signal, evenwhen no power is delivered through the electric power line.